Why did Ford start using a returnless fuel system with the 4.6's.? Didn't all the 5 liters have return style fuel systems?
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Why did Ford go returnless?
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97gtconv.
Member
I know the 98's had something different to their fuel system but I don't remember specifics. Sorry
caballo
I'm the bastard love child of a threesome gone awr
ToplessStang
Member
One reason is that the fuel stays cooler. On a returnless fuel system, you only send the fuel you need to the fuel rail where as in a return type system you'd have extra fuel that is warmed from the engine bay go back to the fuel tank. Cooler fuel reduces the chances of vapor lock in the fuel line.
caballo
I'm the bastard love child of a threesome gone awr
ToplessStang said:
And emissions?!
Please say emissions. I really want one of the reasons to be emissions, cause I don't know anyother answer and yours sounded so good and like the logic could be used to answer emissions.
J/k (too much caffiene)
trinity_gt
10 Year Member
What is always Ford's primary motivation?
To reduce cost.
The returnless system eliminates the fuel return line, hoses, and fittings, as well as a fuel pressure regulator. In exchange, this system requires just a fuel pressure sensor.
Actually, the fuel injected into the cylinders is cooler with a return-type system, as long as the pressure regulator is located at the opposite end of the fuel rails from the supply hose. This is because fresh cool fuel is constanty being circulated instead of being retained in the fuel rail to be heated by the engine.
The best of theses systems (like that used by Nissan) have a separate feed and return line to each individual injector to further reduce fuel heating. The small amount of heat added to the circulating fuel will not appreciably affect the temperature of the fuel in the tank.
To reduce cost.
The returnless system eliminates the fuel return line, hoses, and fittings, as well as a fuel pressure regulator. In exchange, this system requires just a fuel pressure sensor.
Actually, the fuel injected into the cylinders is cooler with a return-type system, as long as the pressure regulator is located at the opposite end of the fuel rails from the supply hose. This is because fresh cool fuel is constanty being circulated instead of being retained in the fuel rail to be heated by the engine.
The best of theses systems (like that used by Nissan) have a separate feed and return line to each individual injector to further reduce fuel heating. The small amount of heat added to the circulating fuel will not appreciably affect the temperature of the fuel in the tank.
ToplessStang
Member
By the way, I didn`t just invent my post. I`m a Ford tech specialized in engine driveabilty and that is what we were told at the training course 
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HandofDoom_
Banned
trinity_gt
10 Year Member
n0v8or said:
But it also needs a fairly complex fuel pump driver module that replaces a dead-simple, dead-cheap relay. (The PCM varies fuel pressure by varying the speed of the fuel pump via this module.) In terms of cost, it'd seem about a wash: replace a FPR with a pressure sensor and replace a relay with a FPDM. The additional wiring, connectorization and whatnot probably offsets the cost of a relatively cheap length of formed tube running back to the tank.
I think the concern in terms of emissions with the return system is that fuel that enters the hot fuel rails and engine bay and then circulates back to the tank heats the whole of the fuel supply which can increase evaporative emissions.
You'd be surprised the lengths car makers will go to reduce emissions where ever they can. Witness the 2005 Mustang's "emissions trap" in the intake tract designed to absorb and hold hydrocarbon emissions from the intake manifold after the engine is has been shut off.
FallenPhoenix
New Member
ToplessStang said:By the way, I didn`t just invent my post. I`m a Ford tech specialized in engine driveabilty and that is what we were told at the training course
good to get it straight from the source
caballo
I'm the bastard love child of a threesome gone awr
Regarding the Fuel Pump driver Module, you have to consider relative costs from Ford's point of view.
A fuel pump relay and fuel pump PWM (pulse width modulator) module costs Ford approximately the same. I know because I participated in the design of the latter. The solid state module is more robust and can operate reliably at battery voltages from cold start cranking (5V) to a double battery AAA jump start (24V). It takes a relatively expensive relay to match that feat. In addition, the PWM module can feed back diagnostic information to the powertrain computer at an incremental cost of literally pennies.
Where the PWM module really wins is when Ford sells you a replacement part. The price they can charge for the relay is constrained by free market forces; it is easy for aftermarket competitors to make replacements, and competition holds the prices down. On the other hand, the PWM module is a custom part made exclusively for Ford, and uses a custom Integrated Circuit not available to the public (or competitors). So Ford can charge 10X their cost for this module.
It's all about cost and profit.
A fuel pump relay and fuel pump PWM (pulse width modulator) module costs Ford approximately the same. I know because I participated in the design of the latter. The solid state module is more robust and can operate reliably at battery voltages from cold start cranking (5V) to a double battery AAA jump start (24V). It takes a relatively expensive relay to match that feat. In addition, the PWM module can feed back diagnostic information to the powertrain computer at an incremental cost of literally pennies.
Where the PWM module really wins is when Ford sells you a replacement part. The price they can charge for the relay is constrained by free market forces; it is easy for aftermarket competitors to make replacements, and competition holds the prices down. On the other hand, the PWM module is a custom part made exclusively for Ford, and uses a custom Integrated Circuit not available to the public (or competitors). So Ford can charge 10X their cost for this module.
It's all about cost and profit.
trinity_gt
10 Year Member
n0v8or said:
Really? I mean, a relay is a coil, an armature and a high-current contact. By passing a current through the coil you pull the high-current contacts together (or apart...) and that's it. I'm not certain how a device with a logic section, a timing section and a high-current solid state switching element (some sort of MOSFET I'll assume) along with the necessary snubbing and interface circuit, plus the multi-pin connector and a fancy enclosure:
can be the same cost as this:
Hmm. Well, a relay is a switch. About the only thing one needs to be careful of with that is limiting the coil current. But if you've got electronics in that module, then you've also got a dedicated PWB, voltage regulation internally for the logic and things like polarity protection.
And you say all that is still cheaper than this:
The ECM in my old 1988 Cavalier Z24 was able to monitor fuel pump voltage with an ATD input. That allowed the ECM to know the health of the relay and pump.
And it was probably simpler - a wire running to the PCM from the pump - than the logic required to formulate a PWM signal back to the PCM in the FPDM.
Can't argue there. Ford's pretty good at hosing those seeking service or parts. Witness the quote I recently got of $850 (at $97/hr) to install a set of FRPP gears in my 02 MGT...
But I still don't buy that this custom ASIC, PWB, development R&D, packaging, EMI/EMC hardening and all the rest come cheaper to Ford than this:
You're all wrong 
They went to the returnless system so the fuel won't get worn out. With a returnsystem the fuel has to travel all the way to the engine compartment and back hundreds of times before it gets ignited and gets to go to allah. If you had to walk to the front of your car then to the back and back hundreds of times, would you really feel like giving it your all when you're supposed to ignite into a furious explotion, no you will probably just say **** it and go poof.
They went to the returnless system so the fuel won't get worn out. With a returnsystem the fuel has to travel all the way to the engine compartment and back hundreds of times before it gets ignited and gets to go to allah. If you had to walk to the front of your car then to the back and back hundreds of times, would you really feel like giving it your all when you're supposed to ignite into a furious explotion, no you will probably just say **** it and go poof.
trinity_gt
10 Year Member
Rekokulous said:You're all wrong
They went to the returnless system so the fuel won't get worn out. With a returnsystem the fuel has to travel all the way to the engine compartment and back hundreds of times before it gets ignited and gets to go to allah. If you had to walk to the front of your car then to the back and back hundreds of times, would you really feel like giving it your all when you're supposed to ignite into a furious explotion, no you will probably just say **** it and go poof.
Oh.
hotdog71
Member
ok,
So why does this system loose so much pressure 15psi at higher 3500 RMP's which in turn causes the car to run lean which can also cause pinking or pinging which will cause damage to your engine.....
Was this part of Ford's ECO friendly cost saving plan
So why does this system loose so much pressure 15psi at higher 3500 RMP's which in turn causes the car to run lean which can also cause pinking or pinging which will cause damage to your engine.....
Was this part of Ford's ECO friendly cost saving plan
hotdog71 said:ok,
So why does this system loose so much pressure 15psi at higher 3500 RMP's which in turn causes the car to run lean which can also cause pinking or pinging which will cause damage to your engine.....
Was this part of Ford's ECO friendly cost saving plan
The system does not loose pressure at 3500 rpms.
The returnless fuel system is really pretty neat. It also has it's drawbacks.
You really have to know what you are doing to mess with it.
Pull out your controls system engineering book and read about closed loop control.
Returnless fuel system:
-Differential fuel pressure sensor (fp and manifold absolute vaccum)
-ECM reads differential FP
-ECM inputs the FP into a control loop (probably a PID loop)
-ECM control loop outputs a duty cycle to the FP driver module.
-FP driver module creates a DC PWM (pulse width modulation) output to the FP (ie. it varies the DC voltage)
-FP responds to the varying voltage by speeding up or slowing down (inc or dec pressure)
Then the whole cycle starts over probably 100+ times a second...
http://www.kennebell.net/techinfo/general-info/jimbells-supercharged-perf-guide.pdf
Read the article on the right hand side, that should explain the decision to go returnless.
Read the article on the right hand side, that should explain the decision to go returnless.
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